Research Area 4 - Microbial Community Diversity Shift as Environmental Biosensor

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A ​​recent study (Guo et
al. 2010) shows that farming practices in China are acidifying the nation's
soils and threatening long term productivity at a time when food concerns
worldwide have never been higher. Chinese agriculture has intensified greatly
since the early 1980s on a limited land area with large inputs of chemical
fertilizers and other resources. The rates of nitrogen applied in some regions
are extraordinarily high as compared with those of North America and Europe.
These have degraded soils and environmental quality in the many areas in China.
With high agricultural intensity, comes the use of pesticides which could be
detrimental to soil and water quality. Soil
treatments that affect soil pH may lead to changes in soil microbial
communities which mediate many processes essential to the productivity and
sustainability of soil. Deng and Tabatabai (1996a.b, 1997) reported that these
management systems influence the soil enzymes involved in C, N, S, and P
cycling. Most microorganisms proliferate in neutral soil, thus any
activity that would lead to acidic soil pH is detrimental to vast population of
microorganism. Understanding of microbial properties such as biomass, activity,
and diversity are important in furthering knowledge of the factors contributing
to soil health, and result of such analysis may also be useful to farmers in
devising practical measures of soil quality (Hill et al. 2000), and increase C
sequestration thus minimizing global warming.

In 2010 the Chinese government released a national pollution survey
which revealed a surprisingly high link between water pollution and
agricultural and forest practices, such as overuse of fertilizer and pesticides
(Guo et al. 2010). The enzymes present in soils are dependent on the
functioning of soil microorganisms and their activity not only reflects soil
fertility, but also reflects soil conditions and microbial populations (Chenge
et al. 2002). Because microbes are at the bottom of the food chain, they will
be the first to response to environmental changes. Microbial community biomass, respiration, N
mineralization rate, and fungal abundance have been reported to increase with
greater plant diversity (Zak et al. 2003).
Seasonal and temporal variations in nutrients or physical conditions may
affect the microbial community and diversity leading to difficulties in data
interpretation and meaningful conclusions. Surveying microbial communities and
diversities and studying their processes can be use as a biosensor to predict
the changing environment.

The objectives of this
study are to (i) assess microbial population, (ii) investigate microbial
processes, and (iii) identify and quantify enzymatic activity in selected
urban, agriculture, and forest ecosystems. The study will establish (a) link
between ecosystem disturbance and microbial diversity, (b) microbial processes
and global warming, and (c) nutrient cycling and enzyme activities. Culturable
microbial community/diversity will be evaluated using the most probable number
(MPN) method and plate count (De Leij et
al.1993) whereas the unculturable community will be evaluated by analyzing soil
DNA extracted using Ultraclean Soil DNA kit (Mo Bio Laboratories, CA).
Microbial processes will be evaluated using chloroform fumigation method, and
potential enzyme activities will be assayed based on Tabatabai (1994) and
Tazisong et al. (2008). The REU students will be given hands-on training on
molecular (DNA fingerprinting) and traditional (culture based) techniques used
for surveying soil microbial organisms in environmental samples. The students
will also be exposed on the use of state-of-the-art instrumentation in
quantifying and qualifying these organisms. ​